The present invention concerns the field of communication devices and in particular the field of digital voice and data communication systems. The invention is especially suited for use in wireless telephone devices such as cordless (short range) and mobile (cellular, wide range) telephones.
A recent development in the field of digital communication technology is the introduction of inexpensive, short range radio links. Especially the Bluetooth system offers a low power radio communication link for the transmission of both voice and data. Bluetooth is a universal radio interface in the unlicensed ISM frequency band (2.45 GHz) that enables portable electronic devices to connect and communicate via ad hoc networks. A frequency hop, time division duplex (FH/TDD) scheme is used to reduce the effects of possible interference from other radio sources. The transmission properties of each channel can be adjusted in a number of ways. This includes different data rates, error correction methods, and link protocols. Furthermore, different data packet protocols and voice encoding schemes may be selected.
Further information about the Bluetooth system can be found in the article xe2x80x9cBLUETOOTHxe2x80x94The universal radio interface for ad hoc, wireless connectivityxe2x80x9d by Jaap Haartsen, Ericsson Review No. 3, 1998, pages 110-117 and at the Internet site http://www.bluetooth.com. The Bluetooth draft standard and the underlying IEEE specification P802.11/D10: xe2x80x9cWireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specificationsxe2x80x9d provide detailed information about all features of the Bluetooth system. These documents are incorporated into the present specification in their entirety.
On page 112 of the article by Jaap Haartsen cited above, a xe2x80x9cthree-in-one phonexe2x80x9d is mentioned as a possible user scenario of the Bluetooth system. This telephone may function as an intercom at the office (no telephony charge), as a cordless phone at home (fixed-line charge), and as a mobile phone otherwise (cellular charge). No technical information is given as to the way in which this functionality may be achieved.
A plurality of problems arise when the Bluetooth technology is used to build portable telephone and data transmission devices. These problems include achieving low power consumption of the mobile station, achieving quick response times when calls or data transmissions are originated, and negotiating appropriate properties of the Bluetooth transmission channel.
Technical Report TR 101 176 V1.1.1. of the European Telecommunications Standards Institute (ETSI) titled xe2x80x9cDigital Enhanced Cordless Telecommunications (DECT); Global System for Mobile communications (GSM); Advanced integration of DECT/GSM dual-mode terminal equipmentxe2x80x9d teaches an integration of the two systems GSM and DECT. This solution is difficult because essentially two different terminals have to be integrated into one device. A DECT/GSM dual-mode terminal is also bound to be expensive since a DECT terminal costs about as much as a GSM mobile.
It is an object of the present invention to avoid at least some of these problems and to provide a way of establishing a communication link between a telecommunications network and a mobile station that is especially adapted for portable telephone and data transmission devices. Preferably, the whole system should also be flexible and easy to use as well as easy to implement with no or little hardware expense.
This objective is achieved by a method and devices having the features of the independent claims. The dependent claims define preferred embodiments of the present invention.
The invention is based on the idea to execute, before a call indication is received from the telecommunications network, a preliminary step in which at least one property of the short range radio channel is negotiated. The mobile station then enters a power saving mode. When the actual call indication arrives, the mobile station is activated and linked to the telecommunications network using the at least one negotiated channel property.
The invention provides several advantages. Since the mobile station enters the power saving mode after the preliminary step discussed above, low average power consumption and long battery life is achieved. Furthermore, the preliminary negotiation step may be rather time consuming, especially if it includes a further step of identifying available mobile stations. Since this step, according to the invention, is performed before the actual call indication arrives, the response time from arrival of the call indication to establishment of the communication link is shortened considerably. This is very convenient in the case of telephone (voice) connections and may be indispensable for the exchange of data packets. Furthermore, there is enough time for the preliminary negotiation step to find an optimal set of channel parameters. This may include time consuming operations, for example determining an optimal transmission power level depending on the level of noise signals in the environment.
In the terminology used here, a xe2x80x9cproperty of the radio channelxe2x80x9d may be any property or setting that affects the communication process via the channel. This includes properties of the transceivers of the local and mobile stations as well as properties of the method used in controlling said transceivers. The term xe2x80x9cnegotiatingxe2x80x9d includes all kinds of communication processes, for example any request/response process having one or more steps as well as any issuing of one or more commands for setting one or more channel properties concurrently or sequentially.
In preferred embodiments of the invention, a property of the radio channel that may be negotiated is the transmission power level of one or both radio transceivers in the local and/or the mobile stations. This property may be used to determine the range or area for the short range radio channel. The short range radio channel may have a maximum range of 500 m or 200 m or 100 m or 50 m or less in some embodiments. of the invention. Other variable properties of the channel are the voice transmission quality and/or protocol, the data transmission rate and/or protocol, and the error correction and/or recovery method. The possible settings of the channel may be according to a single standard or a combination of standards. For example, a GSM voice transmission method may be used in the context of a Bluetooth short range radio link.
Further properties of the local station and/or the mobile station may be negotiated in preferred embodiments. For example, a possible property of the local station is the priority of the local and mobile stations with respect to the signaling of incoming call indications.
Preferably the invention also provides a procedure for the mobile station to initiate an outgoing communication. This procedure may comprise the step of trying to contact the local station, and if this fails, using a further radio channel for establishing the communication link. The further radio channel preferably may be a long range and/or cellular radio channel, in particular a GSM channel.
The invention can be used with all kinds of short range radio channels having at least one adjustable property. In preferred embodiments, the short range radio channel is a digital channel and/or employs frequency hopping and/or time division multiplexing. In preferred embodiments, the short range radio channel is a point-to-point channel in a non-cellular environment. The short range radio channel may use a spread spectrum transmission method, which preferably includes channel hopping at a high hopping frequency (preferably above 500 hops/second or above 1000 hops/second or about 1600 hops/second). It is preferred to use a channel according to the Bluetooth standard mentioned initially as the short range radio channel. It is further preferred that the telecommunication network is a wire-based public or local network.
A mobile station according to a preferred embodiment of the invention is a GSM handset having an additional Bluetooth radio transceiver.